In wireless communications networks, several possible features such as hierarchical cell structures, frequency diversity scheduling, and frequency selective scheduling make use of the speed of a wireless device connected to the base station.
The speed of a wireless device may be useful when utilizing hierarchical cell structures. Hierarchical cell structures are a means by which a different types of cells with different coverage areas may be overlapped. A cell with a larger coverage area with relatively less capacity may overlap a cell with a smaller coverage area with relatively higher capacity. The cell with a smaller coverage area itself may overlap a cell with yet a still smaller coverage area with a relatively even higher capacity. A cell with a larger coverage area may overlap many cells with smaller coverage areas. The cell connected to a wireless device may be reselected to another cell in the hierarchy based on the capacity needs, status, or location of the device. The hierarchical cell structures may be prioritized for a wireless device being served by the structure. The prioritization may take into account the speed of the wireless device. For example, a relatively fast moving wireless device may be unable to sustain a connection while in a smaller coverage area without triggering multiple handoffs, causing performance problems. A fast moving wireless device may be assigned to cells with larger coverage areas, and slow moving wireless devices may be assigned to cells with smaller coverage areas. A related issue is that the speed determination should happen quickly, to adapt, for example, to a wireless device in car accelerating from stop and move the wireless device from a small-coverage-area to a large-coverage-area cell. Thus, determining the speed of a wireless device is useful when utilizing hierarchical cell structures.
The speed of a wireless device may also be useful when utilizing frequency diversity scheduling or frequency selective scheduling. In wireless communication, frequency diversity scheduling is a method of assigning random subcarriers to subchannels, which results allows the system to handle a wider range of conditions. Frequency selective scheduling is a method of determining the optimal subchannel on physically adjacent subcarriers to be assigned to a wireless device. Frequency selective scheduling can provide greater throughput capacity over frequency diverse scheduling, but requires more overhead.
Frequency selective scheduling is effective for slow-moving wireless devices. For wireless device speeds exceeding a certain threshold, channel conditions change too quickly for the wireless network and the wireless device to keep up. The channel condition information obtained from the sub-band Channel Quality Indicator (“CQI”) reported by the wireless network becomes out-of-date by the time the wireless network actually receives packet delivery. The gain of using frequency selective scheduling disappears. For this reason, fast moving wireless devices often use frequency diversity scheduling, and slow moving wireless devices often use frequency selective scheduling. Thus, the speed of a wireless device is useful when using either frequency diversity scheduling or frequency selective scheduling.